Composite materials are increasingly used in a variety of industries, including the automobile, aerospace, marine, and consumer products markets. Composite materials are broadly defined as structures which comprise two or more different materials, such as glass fibers embedded in an epoxy resin or graphite fibers embedded in an epoxy resin. Other combinations are well known to those of ordinary skill in the art. A variety of plastic resins other than epoxy are also used as one component of the composite.
In general, structures manufactured from composite materials, such as panels, I-beams, T-beams, and other more convoluted shapes comprise a plurality of layers of uncured or partially cured composite plies. The plies are usually supplied in a continuous form resembling a roll of tape which is then cut to the desired length. The plies may be tacky at room temperature, as in the case of thermosetting resins, or nontacky (i.e., slippery), as in the case of thermoplastic resins. In either case, after the plies have been laid up on a forming tool, the resin must be cured and the laminate stack debulked to form a consolidated panel, I-beam, T-beam, etc. Some composite materials, typically the fiberglass/resin composites, cure at room temperature. In a preferred method, especially in the aerospace industry, where graphite fiber/epoxy resin composites are common, curing at elevated temperatures and pressures is achieved in an autoclave.
In an autoclave curing process, a plurality of tacky layers of composite material are laid up one on top of another. The composite materials may be partially debulked by hand, such as with a roller. After the entire composite stack has been laid up on a forming tool, a layer of flexible material, commonly referred to as a "vacuum bag," is sealed to the forming tool about the periphery of the composite lay up. The forming tool, composite part, and vacuum bag assembly is then positioned in an autoclave, where the entire assembly is processed at elevated temperatures and pressures.
During the autoclave procedure, the volume between the vacuum bag and forming tool is evacuated to remove as much gas as possible from between the layers of composite material and to at least partially debulk the laminate stack. For this purpose, vacuum bag probes, such as those shown in FIGS. 5 and 6, are applied to a vacuum bag in the manner shown in FIG. 1.
Probes of this type have a base plate or base section 10, 12 which is positioned underneath the vacuum bag, on top of a breather layer 13, which is positioned above the composite layers 14 and above a portion of the forming tool 16 which surrounds the periphery of the composite layers. The vacuum bag 18 is provided with a vacuum bag aperture 20 so that base apertures 24 and 26 (see FIGS. 5 and 6) can be positioned in registration therewith. The vacuum bag 18 is sealed to the forming tool by a peripheral seal 28, which may take the form of double-sided tape or a resilient silicone gasket.
The probes shown in FIGS. 5 and 6 also have top sections 30, 32, which mate with the base sections 10, 12 so as to form an airtight seal between the base section and vacuum bag, and the vacuum bag and top section. A resilient gasket 34, 36 is typically provided to form a good seal between the vacuum bag and the base plate, while a smooth surface 38, 40 is provided on the underside of the top section 30, 32 to form a good seal between the top section 30, 32 and the vacuum bag 18.
The top sections 30, 32 are provided with mating mechanisms 44, 46, which engage corresponding structures 48, 50 in the base sections 10, 12. The mating mechanisms serve to apply a compressive force between the top and base sections so as to effect at least an initial seal between the top and base sections and the vacuum bag 18. The top sections are also provided with bores 52, 54, which register with the apertures 24, 26 in the bases so that a vacuum can be drawn therethrough from a source 56, shown in FIG. 1.
Substantial disadvantages are associated with each of the prior art probes shown in FIGS. 5 and 6. The mating mechanism 46 and corresponding structure 48 of the probe shown in FIG. 5 is of the bayonet type. That is, the top section 30 is provided with a radially directed, split tool pin 58 which engages opposed female receptacles 60 in the aperture 24 of the base section 10. The aperture 24 is provided with opposed, wedgelike ramps 62 which draw the smooth surface 38 against the gasket 34 when the top section 30 is rotated approximately 90 degrees in a clockwise direction. This structure advantageously permits external air pressure to further force the top section 30 against the base section 10 (see FIG. 1) as air is evacuated from the sealed environment beneath the vacuum bag 18. That is, the bayonet mechanism does not resist the further application of downward pressure from the elevated atmospheric pressure in the autoclave. In this mechanism, the primary sealing function is provided by the pressure differential between the top and base sections rather than by the bayonet mechanism. A very good seal can be effected in this manner. However, the bayonet mechanism itself contributes to a substantially degraded environment which can both ruin the vacuum system and introduce undesirable contaminants into the forming tool environment.
The base 10 is typically machined from a relatively soft aluminum. The split tool pin 58 tends to dig into the ramp 62 because of the relatively small contact surface therebetween. As a result, metal shavings are dislodged from the base 10 and can enter and undesirably contaminate both the vacuum system and the forming tool environment. This result is especially disadvantageous in the aerospace industry, where very high-quality standards must be maintained.
In addition, once the bayonet-style mating mechanism 44 begins to wear, the ability to form an initial vacuum seal between the top and base sections is degraded. The split tool pin 58 also disadvantageously blocks the bore 52 in the top section. A high-pressure, quick-disconnect fitting having a one-way valve is typically threaded on the exposed end 59 of the probe. The check valve may become clogged or sticky. The split tool pin 58 disadvantageously interferes with the insertion of a screwdriver or other device into the bore for manipulation or removal of the one-way valve.
The mating mechanism 46, shown in FIG. 6, overcomes the above-described wear/contamination problem associated with the probe of FIG. 5. However, this probe introduces other disadvantages which severely compromise the integrity of the vacuum seal.
As shown in FIG. 6, the mating mechanism 46 is of the threaded variety. The base section 12 is provided with corresponding threads in the corresponding structure 50. Substantially less wear occurs with this mating mechanism, as opposed to the bayonet-type mating mechanism 44 of FIG. 5, because of the increased contact area between the mating structures. The threaded mating mechanism 46 of the probe shown in FIG. 6 also provides clear access to the bore 54 and thus does not have the access disadvantage associated with the bayonet-style mating mechanism 44 of the probe shown in FIG. 5. However, this threaded-style mating mechanism 46 positively fixes the position of the top section 32 with respect to the base section 12 in the axial direction. As a result thereof, pressure differentials between the base section and top section cannot assist the action of the mating mechanism to further force the smooth surface 40 to the vacuum bag 18, resilient gasket 36, and base section 12.
Technicians using the type of probe shown in FIG. 6 must therefore assure that each and every FIG. 6-type probe is thoroughly tightened down to effect a good seal. Probes are typically provided every nine square feet of area on the vacuum bag 18. Autoclaves are presently available which can process forming tools having dimensions in excess of 20 by 90 feet. Therefore, approximately 200 probes of the type shown in FIGS. 5 and 6 must be applied to the vacuum bag. Failure of any one of the probes (such as by failure to appropriately tighten down one of the probes of FIG. 6) can result in the entire cured composite structure being ruined.
In view of the above, an improved vacuum probe is needed which does not suffer from the contamination and wear problems associated with the probe of FIG. 5, which does not resist the application of secondary compressive forces due to pressure differentials between the top and base sections, as does the probe of FIG. 6, and which provides an unobstructed through-bore to facilitate access to a quick-release valve at the end of the through-bore.
In addition to the above, both the probes of FIGS. 5 and 6 utilize bases 10, 12 which are made from single blocks of aluminum. Grooves 64, 66 must be machined or milled into the bases to provide air passageways from the periphery of the bases to the base apertures 24, 26. The bases are thus relatively expensive. Therefore, in addition to the abovedescribed needs, a need exists for a base section which can be inexpensively constructed with appropriate air passageways.